GRB 250520A
GCN Circular 40490
Subject
Swift GRB 250520A: Global MASTER-Net observations report
Date
2025-05-20T02:56:51Z (10 days ago)
Edited On
2025-05-20T13:19:04Z (9 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB250520.11 (trigger No 1315630,18h 49m 04.32s , -11d 50m 49.2s, R=0.05) errorbox 23 sec after notice time and 46 sec after trigger time at 2025-05-20 02:43:03 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 25 deg. The sun altitude is -33.7 deg.
The galactic latitude b = -5 deg., longitude l = 22 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2875870
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
52 | MASTER-SAAO | C | 10 | 16.3 |
80 | MASTER-SAAO | C | 10 | 16.3 |
115 | MASTER-SAAO | C | 20 | 16.4 |
159 | MASTER-SAAO | C | 30 | 16.7 |
213 | MASTER-SAAO | C | 40 | 16.7 |
277 | MASTER-SAAO | C | 50 | 16.7 |
351 | MASTER-SAAO | C | 60 | 17.0 |
430 | MASTER-SAAO | C | 60 | 16.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 40491
Subject
GRB 250520A: Swift detection of a burst
Date
2025-05-20T02:59:58Z (10 days ago)
From
K.L. Page at U Leicester <klp5@leicester.ac.uk>
Via
email
R. A. J. Eyles-Ferris (U Leicester), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (U Tampa), M. J. Moss (GSFC) and K. L. Page (U Leicester)
report on behalf of the Neil Gehrels Swift Observatory Team:
At 02:42:16.84 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 250520A (trigger=1315630). Swift slewed immediately to the burst.
The BAT on-board calculated location is RA, Dec 282.268, -11.847 which is
RA(J2000) = 18h 49m 04s
Dec(J2000) = -11d 50' 49"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a short burst
with a duration of about 1 sec. The peak count rate
was ~10,000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 02:44:40.8 UT, 144.1 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 282.28588, -11.86811 which
is equivalent to:
RA(J2000) = 18h 49m 08.61s
Dec(J2000) = -11d 52' 05.2"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 98 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at https://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.68 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 8
(+6.16/-4.83) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 148 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the large, but uncertain, extinction
expected.
Burst Advocate for this burst is R. A. J. Eyles-Ferris (raje1 AT leicester.ac.uk).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/)
GCN Circular 40492
Subject
GRB 250520A: Prompt enhanced Swift-XRT position
Date
2025-05-20T03:19:49Z (10 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Using 1.2 ks of promptly downlinked XRT event data for GRB 250520A, we
find an enhanced XRT position of the afterglow: RA, Dec: 282.28613,
-11.86896 which is equivalent to:
RA (J2000) = 18 49 08.67
Dec (J2000) = -11 52 08.3
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/1315630.
Position enhancement is described by Goad et al. (2007, A&A, 476, 1401)
and Evans et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.
GCN Circular 40493
Subject
GRB 250520A: GOTO optical upper limit
Date
2025-05-20T03:28:58Z (10 days ago)
From
Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
The Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022; Dyer et al. 2024) performed a targeted observation in response to Swift/Burst Alert Telescope (BAT)-triggered GRB 250520A (Eyles-Ferris et al. GCN 40491) at 2025-05-20 UT 02:46:48 (4.54 minutes after trigger). The observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings.
No optical counterpart is detected within the Swift/XRT 90% localisation region (Evans et al. GCN 40492) to a 3-sigma limiting magnitude of L > 19.86 (AB).
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 40494
Subject
GRB 250520A: Enhanced Swift-XRT position
Date
2025-05-20T08:03:58Z (9 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1223 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 250520A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 282.28575, -11.86913 which is equivalent
to:
RA (J2000): 18h 49m 8.58s
Dec (J2000): -11d 52' 08.9"
with an uncertainty of 2.5 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 40495
Subject
GRB 250520A: SVOM/GRM observation
Date
2025-05-20T08:40:08Z (9 days ago)
Edited On
2025-05-20T17:02:23Z (9 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Wen-Jun Tan Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Stéphane Schanne (CEA), Marius Brunet (IRAP)
report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a short burst GRB 250520A (SVOM trigger reference: sb25052002) at 2025-05-20T02:42:16.900 UTC (T0), which is also detected by Swift/BAT (R. A. J. Eyles-Ferris et al., GCN #40491).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.34 +0.12/-0.16 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250520A.png
In addition, the position of this burst, as determined by Swift (RA= 282.268, Dec=-11.847, GCN #40491), is located at about 101 degrees from the SVOM optical axis. ECLAIRs was not colecting data at the time of the burst.
With this localization, the time-averaged spectrum from T0-0.1 to T0+0.2 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.64 +/-0.13 and the cutoff energy, parameterized as Epeak, is 1080 +283/-151 keV. The event fluence (10-1000 keV) in this time interval is (2.34 +0.15/-0.14)E-06 erg/cm^2.
The localization of GRB 250520A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/grb250520A_amati.png
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
GCN Circular 40497
Subject
GRB 250520A: AstroSat CZTI detection of a short burst
Date
2025-05-20T09:34:08Z (9 days ago)
From
Gaurav Waratkar at IIT Bombay <gauravwaratkar@iitb.ac.in>
Via
Web form
M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a short duration GRB 250520A which was also detected by Swift/BAT (Eyles-Ferris et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495), and CALET/GBM (Trigger ID 1431743946).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-05-20 02:42:16.94 UTC. The measured peak count rate associated with the burst is 1106 (+638, -259) counts/s above the background in the combined data of two quadrants (out of four), with a total of 73 (+23, -23) counts. The local mean background count rate was 141 (+22, -43) counts/s. Using cumulative rates, we measure a T90 of 0.15 (+0.03, -0.04) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-05-20 02:42:16.12 UTC. The measured peak count rate associated with the burst is 674 (+70, -74) counts/s above the background in the combined data of all quadrants, with a total of 640 (+115, -115) counts. The local mean background count rate was 1161 (+9, -10) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 40498
Subject
GRB 250520A: DDOTI Optical Upper Limit
Date
2025-05-20T10:26:32Z (9 days ago)
From
Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it>
Via
Web form
Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observed the field of the GRB 250520A detected by Swift/BAT (Eyles-Ferris
et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495) and AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 40497) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-05-20 UTC.
DDOTI observed the field of GRB 250520B from 06:59 UTC to 08:48 UTC (from T+4.3 h to T+6.2 h after the trigger) and obtained a total exposure of 22 minutes, alternating with other scientific programs.
Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no any uncatalogued source at the position reported by Fermi GBM Team, GCN Circ. 40314) down to a 3-sigma limiting AB magnitude of:
w > 20.5
This value is consistent with the reported by GOTO (Kumar et al., GCN Circ. 40493)
These values are not corrected for the Galactic extinction.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir.
GCN Circular 40499
Subject
GRB 250520A: COLIBRÍ optical upper limit
Date
2025-05-20T10:34:25Z (9 days ago)
From
Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra@roma2.infn.it>
Via
Web form
Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495) and AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 40497) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-20 06:42 to 06:45 UTC (from 4.0 to 4.1 hours after the trigger) and obtained 3 minutes of exposure in the i filter.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the XRT enhanced position (Goad et al., GCN Circ. 40494) down to the following 3-sigma limit:
i > 21.3
This upper limit is consistent with the non-detection reported by GOTO (Kumar et al., GCN Circ. 40493) and DDOTI (Becerra et al., GCN Circ. 40498).
Further observations and analysis are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 40500
Subject
GRB 250520A：SVOM/VT optical candidate
Date
2025-05-20T10:45:18Z (9 days ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT team:
SVOM performed a Target of Opportunity observation of GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN 40491), SVOM/GRM (Wang et al., GCN 40495) and AstroSat(Tembhurnikar et al., GCN 40497). SVOM/VT began observing the field at 2025-05-20T03:51:16 UTC, 1.15 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
An uncatalogued faint source, compared to PanStarrs catalogue, is found using VT X-band data, within the error box of Swift/XRT (Goad et al., GCN 40494) at RA=282.28578, Dec=-11.86939 degrees:
R.A.(J2000) = 18:49:08.58
Dec.(J2000) = -11:52:09.79
with an uncertainty of 0.5 arcsec.
The source is detected in VT_R only. The magnitude is estimated to be 23.2+/-0.1 mag with an effective exposure time of 37*70 seconds at the mid time of 2.14 hours after the burst.
The photometry was estimated in AB magnitude and not corrected for Galatic extinction.
Give the faintness of the candidate, we cannot determine whether it is fading. More follow-ups are encouraged.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.
GCN Circular 40502
Subject
GRB 250520A: REM optical/NIR early observations
Date
2025-05-20T11:04:40Z (9 days ago)
From
Riccardo Brivio at INAF-OAB <riccardo.brivio@inaf.it>
Via
Web form
R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team:
We observed the field of GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN 40491), SVOM/GRM (SVOM/GRM team, GCN 40495), and AstroSat (Tembhurnikar et al., GCN 40497) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 20 at 02:43:22 UT (i.e. 65 sec after the burst), and lasted for about 3 hours.
From preliminary inspection, we do not detect any possible counterpart at the position of the optical candidate (Xin et al., GCN 40500), within the Swift/XRT enhanced position (Goad et al., GCN 40494), down to the following 3sigma limits:
r > 17.7 (AB; calibrated against the Pan-STARRS catalogue),
at a mid-time of 70 sec after the trigger;
H > 15.1 (Vega; calibrated against the 2MASS catalogue),
at a mid-time of 113 sec after the trigger.
GCN Circular 40503
Subject
GRB 250520A: Swift-XRT refined Analysis
Date
2025-05-20T14:29:54Z (9 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), M.A. Williams
(PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), B.
Sbarufatti (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT
team:
We have analysed 6.7 ks of XRT data for GRB 250520A, from 127 s to 34.5
ks after the trigger. The data comprise 16 s in Windowed Timing (WT)
mode (the first 9 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode.
The light curve can be modelled with a power-law decay with a decay
index of alpha=2.35 (+0.23, -0.22).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.4). The
best-fitting absorption column is 1.3 (+0.5, -0.4) x 10^22 cm^-2, in
excess of the Galactic value of 3.7 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 5.0 x 10^-11 (1.1 x 10^-10) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.3 (+0.5, -0.4) x 10^22 cm^-2
Galactic foreground: 3.7 x 10^21 cm^-2
Excess significance: 3.6 sigma
Photon index: 2.1 (+/-0.4)
If the light curve continues to decay with a power-law decay index of
2.35, the count rate at T+24 hours will be 10.0 x 10^-7 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.0 x
10^-17 (1.1 x 10^-16) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01315630.
This circular is an official product of the Swift-XRT team.
GCN Circular 40504
Subject
GRB 250520A: Gemini-South optical observations
Date
2025-05-20T16:07:09Z (9 days ago)
From
Jillian Rastinejad at Northwestern Univ. <jillianrastinejad2024@u.northwestern.edu>
Via
email
Jillian Rastinejad, Wen-fai Fong, and Charlie Kilpatrick (Northwestern) report on behalf of a larger collaboration:
We observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491) with the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South under Program GS-2025A-Q-112 (PI: Fong). We obtained 15x120-sec imaging in i-band starting at 2025-05-20 03:45:39.2 UT (1.06 hrs post-burst), at a median airmass of 1.8 and seeing of 0.7''.
We detect a clear source coincident with the candidate optical counterpart discovered by SVOM (Xin et al., GCN 40500) that is within the enhanced XRT localization (Goad et al., GCN 40494). Calibrated to Pan-STARRS DR2 (Flewelling et al., 2020, ApJS, 251, 7), we measure a magnitude for this source of i = 22.4 +/- 0.2 AB mag. This value does not include a correction for Galactic extinction, which is significant (A_V = 2.1 mag; Schlafly and Finkbeiner 2011, ApJ, 737, 103).
The brightness of this source is consistent with reported upper limits (Brivio et al. GCN 40502, Pereyra et al., GCN 40499, Becerra et al. GCN 40498, Kumar et al. GCN 40493). Correcting our measurement and the value reported by SVOM at 2.14 hours post-burst (VT_R = 23.2 +/- 0.2 mag; Xin et al., GCN 40500) for Galactic extinction, we find no clear evidence for fading within the uncertainties.
At or very close to the position of the SVOM and Gemini source, there appears to be a faint source in i- and z-band archival PS1 imaging (Flewelling et al., 2020, ApJS, 251, 7), though more precise astrometry is needed to determine their relative positions. However, forced photometry near the position of the SVOM source (Xin et al., GCN 40500) in the PS1 images yields 3-sigma upper limits on underlying emission of i > 22.2 and z > 21.7 AB mag, uncorrected for extinction. Given that the PS1 i-band limit is shallower than our source magnitude, it is difficult to tell whether the faint source was pre-existing or is the afterglow of GRB 250520A.
Further observations are planned to assess the variability of the source and others in the field. We thank the Gemini staff for the rapid scheduling and execution of these observations.
GCN Circular 40505
Subject
GRB 250520A: J-band observations with WINTER
Date
2025-05-20T18:00:54Z (9 days ago)
From
Geoffrey Mo at MIT <gmo@mit.edu>
Via
Web form
Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations were triggered automatically and began at 2025-05-20T07:26:08 UTC (4.7 hours after the GRB), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar
(https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We do not detect any uncataloged sources at the SVOM/VT optical candidate location (Xin et al., GCN 40500) or in the Swift/XRT localization (Evans et al., GCN 40492; Goad et al., GCN 40494; Perri et al., GCN 40503), after visual comparison to archival VISTA Hemisphere Survey J-band imaging (McMahon et al. 2013). This is consistent with observations by Lipunov et al., GCN 40490; Eyles-Ferris et al., GCN 40491; Kumar et al., GCN 40493; Becerra et al, GCN 40498; Pereyra et al, GCN 40499; Brivio et al., GCN 40502; and Rastinejad et al., GCN 40504. We obtain the following 5-sigma upper limit: J ~ 18.5 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 40509
Subject
GRB 250520A: Swift/UVOT Upper Limits
Date
2025-05-21T13:02:53Z (8 days ago)
From
Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>
Via
email
S. R. Oates (Lancaster U.) and R. A. J. Eyles-Ferris (U. Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250520A
127 s after the BAT trigger (Eyles-Ferris et al., GCN Circ. 40491).
No optical afterglow consistent with the enhanced XRT position (Goad et al., GCN Circ. 40494)
or the SVOM/VT optical candidate (Xin et al., GCN Circ. 40500) is detected in
the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL
white 149 298 147 >20.9
white 149 1373 392 >21.3
v 127 1251 110 >18.9
b 481 1349 97 >19.7
u 456 1324 97 >19.3
uvw1 432 1300 97 >19.1
uvm2 407 1275 78 >18.6
uvw2 358 1394 112 >19.2
We caution that the photometry may not be accurate, as the source region
used to determine the optical/UV limits, is on an area of the UVOT
detector with low sensitivity. The magnitudes in the table are not corrected
for the Galactic extinction due to the reddening of E(B-V) = 0.754 in the
direction of the burst (Schlegel et al. 1998).
GCN Circular 40511
Subject
GRB 250520A: VLT/FORS2 Optical Observation
Date
2025-05-21T14:13:02Z (8 days ago)
From
Yu-Han Yang at University of Rome Tor Vergata <yyang@roma2.infn.it>
Via
Web form
Yu-Han Yang (U Rome), Rosa L. Becerra (U Rome) and Eleonora Troja (U Rome) report on behalf of the ERC BHianca team:
We observed the field of GRB 250520A (Eyles-Ferris et al., GCN 40491) with the FORS2 imager on the ESO VLT UT1 (Antu). Observations began 27.8 hours after the trigger and were carried out in the R filter with an average airmass of ~1.
We detect the source previously reported as a candidate from SVOM/VT (Xin et al., GCN 40500) with a preliminary magnitude of R~23 AB mag, calibrated using nearby stars from the Pan-STARRS DR2 (Flewelling et al., 2020, ApJS, 251, 7), uncorrected for Galactic extinction. Compared to the magnitude reported by SVOM/VT (Xin et al., GCN 40500), we find no evidence of fading.
No other source is detected within the XRT error circle (Goad et al. GCN 40494) down to R>24.6 (3-sigma).
We thank the staff at the VLT for the rapid execution of these observations.
GCN Circular 40512
Subject
Konus-Wind detection of GRB 250520A (short/hard)
Date
2025-05-21T14:42:50Z (8 days ago)
Edited On
2025-05-22T14:10:09Z (7 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Dmitry Frederiks at Ioffe Institute <ddfrederiks@gmail.com>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The short GRB 250520A (Swift detection: Eyles-Ferris et al., GCN 40491;
SVOM/GRM observation: Wang et al., GCN 40495; AstroSat CZTI detection:
Tembhurnikar et al., GCN 40497)
triggered Konus-Wind (KW) at T0=9741.866 s UT (02:42:21.866).
The burst light curve shows a single pulse,
which starts at ~T0-0.07 s and has a duration of ~0.26 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250520_T09741/
As observed by Konus-Wind, the burst had the total fluence
of (3.38 ± 0.75)x10^-6 erg/cm^2 and a 16-ms peak energy flux,
measured from T0-0.032, of (3.49 ± 0.81)x10^-5 erg/cm^2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst (measured from T0 to T0+0.192 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -0.48 (-0.27,+0.41),
the high energy photon index beta = -2.51 (-1.99,+0.47),
the peak energy Ep = 671 (-211,+247) keV,
chi2 = 37/27 dof.
The spectrum near the peak count rate (measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -0.67 (-0.27,+0.46),
the high energy photon index beta = -2.39 (-7.61,+0.53),
the peak energy Ep = 1099 (-505,+876) keV,
chi2 = 11/17 dof.
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.
GCN Circular 40518
Subject
GRB 250520A: 10 GHz VLA radio source
Date
2025-05-22T02:15:16Z (8 days ago)
From
Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>
Via
Web form
G. Schroeder (Cornell), J. Rastinejad, W. Fong (Northwestern), T. Laskar (Utah) report:
We observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497; Frederiks et al., GCN 40512) with the Karl G. Jansky Very Large Array (VLA) in D->C configuration under program 25A-063 (PI Schroeder) at a mid time of 2025 May 21 at 09:22 UT (1.28 days post-burst) for 1.25 hours at a mean frequency of 10 GHz.
In preliminary analysis, we detect a 4-sigma radio source with a flux density of ~18 microJy at the position:
RA(J2000) = 18:49:08.57
Dec(J2000) = -11:52:07.7
with an uncertainty of ~0.8" in each coordinate. This position is consistent with the X-ray position (Goad et al., GCN 40494) but offset (~2") from the optical source reported by Xin et al. (GCN 40500), which has not yet shown any evidence for fading (Yang et al., GCN 40511). At the position of the radio source, we do not detect any optical emission in Gemini i-band imaging (Rastinejad et al., GCN 40504). Further observations are planned to assess the variability of the radio source and its connection, if any, to GRB 250520A.
We thank the VLA staff for quickly approving and executing these observations.
GCN Circular 40519
Subject
GRB 250520A: CALET Gamma-Ray Burst Monitor detection
Date
2025-05-22T02:30:45Z (8 days ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), S. Torii, Y. Akaike,
K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The short GRB 250520A (Swift Detection: Eyles-Ferris et al., GCN Circ. 40491;
SVOM/GRM observation: Wang et al., GCN Circ. 40495; AstroSat CZTI detection:
Tembhurnikar et al., GCN Circ. 40497; Konus-Wind detection: Frederiks et al.,
GCN Circ. 40512) triggered the CALET Gamma-ray Burst Monitor (CGBM) at
02:42:16.72 UTC on 20 May 2025
(https://cgbm.calet.jp/cgbm_trigger/flight/1431743946/index.html).
The burst signal was seen by all CGBM detectors.
The burst light curve shows a single pulse that starts
at T+0.06 sec, peaks at T+0.19 sec, and ends at T+0.31 sec.
The T90 and T50 durations measured by the SGM data are 0.21 +/- 0.04 sec
and 0.09 +/- 0.01 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1431743946/
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 40540
Subject
GRB 250520A: GRBAlpha detection
Date
2025-05-23T18:30:23Z (6 days ago)
From
Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>
Via
Web form
M. Dafcikova, J. Ripa (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration.
The short-duration GRB 250520A (Swift/BAT detection: GCN 40491; SVOM/GRM detection: GCN 40495; AstroSat/CZTI detection: GCN 40497; Wind/Konus detection: GCN 40512, CALET/CGBM detection: GCN 40519) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract).
The detection was confirmed at the peak time 2025-05-20 02:42:16.5 UTC. The T90 duration measured by GRBAlpha is 0.5 s and the overall significance during T90 reaches 11 sigma.
The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250520A_GCN.pdf
All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/
GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume.
GCN Circular 40545
Subject
GRB 250520A: 10 GHz VLA Afterglow Confirmation
Date
2025-05-24T00:21:19Z (6 days ago)
From
Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>
Via
Web form
G. Schroeder (Cornell), W. Fong (Northwestern), T. Laskar (Utah) report:
We re-observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497; Frederiks et al., GCN 40512; Asaoka et al., GCN 40519; Dafcikova et al., GCN 40540) with the Karl G. Jansky Very Large Array (VLA) in C configuration under program 25A-063 (PI Schroeder) at a mid time of 2025 May 21 at 11:24 UT (3.36 days post-burst) for a total of 2.25 hours at a mean frequencies of 6 and 10 GHz.
The radio source detected in the previous 10 GHz VLA observation at 1.28 days (Schroeder et al., GCN 40518) is no longer detected at 3.36 days, to a 3 sigma limit of 10 microJy. Given the fading of this source, and its positional coincidence with the XRT afterglow (Goad et al., GCN 40494), we consider it to be the radio afterglow of GRB 250520A.
We thank the VLA staff for quickly approving and executing these observations.
GCN Circular 40546
Subject
GRB 250520A: 3 GHz MeerKAT Detection
Date
2025-05-24T00:23:36Z (6 days ago)
From
Genevieve Schroeder at Cornell University <genevieveschroeder@u.northwestern.edu>
Via
Web form
G. Schroeder (Cornell), L. Rhodes (TSI/McGill), W. Fong (Northwestern), A. J. Levan (Radboud and Warwick) report:
We observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491; SVOM/GRM Team, GCN 40495; Tembhurnikar et al., GCN 40497; Frederiks et al., GCN 40512; Asaoka et al., GCN 40519; Dafcikova et al., GCN 40540) with the MeerKAT radio telescope at 3.1 GHz for a total of 2 hours at a mid time of 2025 May 23 at 03:50 UT (3.05 days post burst).
In preliminary analysis, we detect a ~3.4-sigma radio source with a flux density of ~18 microJy consistent with the position of the 10 GHz radio afterglow (Schroeder et al., GCN 40518; GCN 40545) and also with the X-ray afterglow (Goad et al., GCN 40494). Further observations are planned.
We thank the staff at the South African Radio Astronomy Observatory for scheduling these observations.
GCN Circular 40559
Subject
GRB 250520A: Gemini-South optical afterglow detection
Date
2025-05-28T04:33:41Z (2 days ago)
From
Wen-fai Fong at Northwestern University <wfong@northwestern.edu>
Via
Web form
Jillian Rastinejad, Wen-fai Fong (Northwestern), and Genevieve Schroeder (Cornell) report on behalf of a larger collaboration:
We re-observed the location of the short-duration GRB 250520A (Eyles-Ferris et al., GCN 40491) with the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South under Program GS-2025A-Q-112 (PI: Fong). We obtained 20x120-sec imaging in i-band starting at 2025-05-24 04:50:10.7 UT (4.1 days post-burst), at a median airmass of 1.3 and seeing of 0.6". Calibrated to Pan-STARRS DR2 (Flewelling et al., 2020, ApJS, 251, 7), we measure a 3-sigma limiting magnitude of 24.9 AB mag for the image.
We perform image subtraction between our GMOS i-band images observed at 1.06 hours (Rastinejad et al., GCN 40504) and at 4.1 days post-burst. We detect a clear residual coincident within the X-ray position (Goad et al., GCN 40494) and coincident with the radio afterglow position (Schroeder et al., GCNs 40518, 40545) at:
R.A. = 18:49:08.58 (J2000)
Decl. = -11:52:07.9 (J2000)
with an uncertainty of ~0.3". We do not detect any other significant residuals within or around the XRT localization. Given its rapid fading and spatial coincidence with the X-ray and radio afterglows, we consider this source to be the optical afterglow of the short GRB 250520A. We note that this source is distinct from the optical candidate reported previously (e.g., Xin et al., GCN 40500).
Calibrated to Pan-STARRS DR2, we measure a magnitude for the optical afterglow of i = 23.9 +/- 0.2 AB mag, uncorrected for high Galactic extinction (Schlafly and Finkbeiner 2011, ApJ, 737, 103), at 1.06 hours post-burst.
We thank the Gemini staff for the rapid scheduling and execution of these observations.
GCN Circular 40565
Subject
GRB 250520A: Swift-BAT refined analysis
Date
2025-05-28T20:11:35Z (21 hours ago)
From
Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>
Via
Web form
R. Gupta (GSFC), S. D. Barthelmy (GSFC),
R. A. J. Eyles-Ferris (U Leicester), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+200 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250520A (trigger #1315630)
(Eyles-Ferris, et al., GCN Circ. 40491). The BAT ground-calculated position is
RA, Dec = 282.265, -11.852 deg which is
RA(J2000) = 18h 49m 03.6s
Dec(J2000) = -11d 51' 08.6"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 68%.
The mask-weighted BAT light curve exhibits a single pulsed emission.
T90 (15-350 keV) is 0.46 +- 0.15 sec (estimated error including systematics).
The time-averaged spectrum from T-0.33 to T+0.23 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
0.55 +- 0.23. The fluence in the 15-150 keV band is 1.8 +- 0.2 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.54 sec in the 15-150 keV band
is 1.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1315630